Chemistry 105, Chapter 2 Exercises
1. Radon is a radioactive gas that can cause lung cancer. It has been detected in the basements
of some homes. How many protons and neutrons are there in a Rn-220 atom?
2. Selenium is widely sold as a dietary supplement. Write the nuclear symbol for naturally
occurring selenium which has 34 protons and 46 neutrons.
3. How do the isotopes N-14 and N-15 differ from each other? How are they similar? Write
nuclear symbols or both.
4. For Uranium-235 indicate the following:
a. the number of protons in the nucleus.
b. the number of neutrons in the nucleus.
c. the number of electrons in the atom.
d. the number of neutrons, protons, and electrons in the U2+ ion formed from this isotope.
5. For Selenium-75 indicate the following:
a. the number of protons in the nucleus.
b. the number of neutrons in the nucleus.
c. the number of electrons in the atom.
d. the number of neutrons, protons, and electrons in the Se2- ion formed from this isotope.
6. Complete the following table:
Nuclear
Symbol
7
Li
Charge
Atomic
Number
Mass
Number
-3
7
14
+4
-2
16
32
Number of
Protons
Number of
Electrons
Number of
Neutrons
26
23
30
25
Mg2+
64
30Zn
14
14
7. How many nonmetals are in the following periods?
a. period 2
b. period 4
c. period 6
8. Which period of the periodic table
a. has no metals?
b. has no nonmetals?
9. Which group in the periodic table
a. has one metalloid and no nonmetals?
b. has no nonmetals or transition metals?
c. has no metals or metalloids?
c. has no metals or metalloids?
10. Write the molecular and empirical formulas for the following organic compound.
H
O
O
H
H
O
C
C
C
C
H
H
O
H
Chapter 2, Answers to Exercises
1. 86 protons, 134 neutrons
2. 8034Se
3. N-14 has 7 neutrons whereas N-15 has 8 neutrons. They have the same number of protons and
electrons. Their symbols are 147N and 157N.
4.a. 92
b. 143
c. 92
d. 143 neutrons, 92 protons, 90 electrons
5.a. 34
b. 41
c. 34
d. 41 neutrons, 34 protons, 36 electrons
6.
Nuclear
Symbol
7
Li
56
3+
26Fe
14
37N
25
Mg2+
64
30Zn
28
14Si
32
16S
Charge
0
+3
-3
+2
0
+4
-2
Atomic
Number
3
26
7
12
30
14
16
7.a. 5
b. 3
c. 2
8.a. 1
b. 7
c. 1
9.a. 3
b. 2
c. 7 and 8
10. molecular, C4H6O4; empirical, C2H3O2
Mass
Number
7
56
14
25
64
28
32
Number of
Protons
3
26
7
12
30
14
16
Number of
Electrons
3
23
10
10
30
10
18
Number of
Neutrons
4
30
7
13
34
14
16